U.S. patent number 3,979,062 [Application Number 05/635,278] was granted by the patent office on 1976-09-07 for peripheral water balance control for center pivot irrigation system.
This patent grant is currently assigned to Valmont Industries, Inc.. Invention is credited to Dale A. Christensen, Ronald L. Frankenstein, Carl R. Ostrom.
United States Patent |
3,979,062 |
Christensen , et
al. |
September 7, 1976 |
Peripheral water balance control for center pivot irrigation
system
Abstract
A water balance control for a pivotal end boom connected to the
outer end of a center pivot irrigation system to irrigate
peripheral areas (e.g., corners) beyond the periphery of the
circular area covered by the main conduit of the system; the water
balance control comprises a sensing mechanism for sensing both the
angular position of the boom and its direction of movement
(swing-out or swing-in) relative to the end of the main conduit.
Primary control circuits, actuated by the sensing mechanism, turn
the boom nozzles on and off, depending on the angular position of
the boom; secondary control circuits, also actuated by the sensing
mechanism, operate the primary controls in accordance with two
different programs, one for swing-out movement and the other for
swing-in movement. A speed control for the main conduit, also
actuated by the sensing mechanism, is included.
Inventors: |
Christensen; Dale A. (Omaha,
NB), Ostrom; Carl R. (Omaha, NB), Frankenstein; Ronald
L. (Fremont, NB) |
Assignee: |
Valmont Industries, Inc.
(Valley, NB)
|
Family
ID: |
24547151 |
Appl.
No.: |
05/635,278 |
Filed: |
November 26, 1975 |
Current U.S.
Class: |
239/11;
239/729 |
Current CPC
Class: |
A01G
25/092 (20130101) |
Current International
Class: |
A01G
25/09 (20060101); A01G 25/00 (20060101); B05B
017/04 (); B05B 003/18 () |
Field of
Search: |
;239/177,212,163-166,76,11 ;137/344 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Ward, Jr.; Robert S.
Attorney, Agent or Firm: Kinzer, Plyer, Dorn &
McEachran
Claims
We claim:
1. A water balance control for a center pivot irrigation system of
the kind including an elongated main conduit assembly having an
inner end pivotally connected to a water source at a central pivot
point and having a plurality of discharge nozzles at spaced
intervals along its length, main drive means for moving the main
conduit assembly around the pivot point to irrigate a primary field
area of circular configuration, an elongated auxiliary conduit
assembly having an inner end connected to and movable with the
outer end of the main conduit assembly and having a series of
discharge nozzles at spaced intervals along its length, and
auxiliary drive means for moving the auxiliary conduit assembly
over a range between a fully retracted position and a fully
extended position, relative to the main conduit assembly, to
irrigate at least one secondary field area beyond the periphery of
the primary field area, the water balance control comprising:
sensing means for sensing movement of the auxiliary conduit
assembly, within its range, relative to the outer end of the main
conduit assembly;
and primary control means, actuated by the sensing means, for
regulating the rate of water discharge from the auxiliary conduit
in accordance with the position of the auxiliary conduit assembly
within its range of movement.
2. A water balance control for a center-pivot irrigation system,
according to claim 1, in which the primary control means comprises
a plurality of flow control valves, each interposed between the
auxiliary conduit and one of the discharge nozzles, and a
corresponding plurality of valve actuators for actuating each flow
control valve, independently of other flow control valves, between
a maximum flow condition and a minimum flow condition, in
accordance with the position of the auxiliary conduit assembly
within its range of movement.
3. A water balance control for a center pivot irrigation system,
according to claim 2, in which each flow control valve is
electrically actuated, in which each valve actuator comprises a
cam-operated electrical switch, and in which the sensing means
comprises a cam shaft, a plurality of valve actuator cams mounted
on the cam shaft and individually associated with respective ones
of the valve actuator switches, and a mechanical linkage
interconnecting the main conduit assembly and the auxiliary conduit
assembly with the cam shaft to rotate the cam shaft in accordance
with movements of the auxiliary conduit assembly relative to the
outer end of the main conduit assembly.
4. A water balance control for a center pivot irrigation system,
according to claim 1, and further comprising secondary control
means actuated by the sensing means, for regulating the rate of
water discharge from the auxiliary conduit nozzles in accordance
with the direction of relative movement of the auxiliary conduit
assembly within its range.
5. A water balance control for a center pivot irrigation system,
according to claim 4, in which the primary control means includes a
first group of primary control circuits for swing-out movement of
the auxiliary conduit assembly and a second group of primary
control circuits for swing-in movement of the auxiliary conduit
assembly, with the main conduit assembly rotating in a given
direction, and in which the secondary control means comprises a
selector switch coupled to the two groups of primary control
switches to select one primary control switch group for operation
at any given time.
6. A water balance control for a center pivot irrigation system,
according to claim 5, in which the primary control means further
comprises a plurality of electrically actuated flow control valves,
each interposed between the auxiliary conduit and one of the
discharge nozzles, with each flow control valve connected to one
primary control circuit of each group, each flow control valve
being actuated to a maximum flow condition by a primary control
circuit from the first group and to a minimum flow condition by a
primary control circuit from the second group, in accordance with
the position of the auxiliary conduit assembly within its range of
movement.
7. A water balance control for a center pivot irrigation system,
according to claim 6, in which each primary control circuit
comprises a cam-operated electrical valve actuator switch, and in
which the sensing means comprises a cam shaft, a plurality of cams
mounted on the cam shaft and individually associated with
respective ones of the valve actuator switches, and a mechanical
linkage interconnecting the main conduit assembly and the auxiliary
conduit assembly with the cam shaft to rotate the cam shaft in
accordance with movements of the auxiliary conduit assembly
relative to the outer end of the main conduit assembly.
8. A water balance control for a center pivot irrigation system,
according to claim 5, in which the sensing means further comprises
a reversing switch for reversing the connections of the selector
switch for a reversal of the direction of movement of the main
conduit assembly.
9. A water balance control for a center pivot irrigation system,
according to claim 1, and further comprising an auxiliary speed
control, coupled to the primary control means, for regulating the
angular speed of the main conduit whenever the system pressure
varies significantly as a result of a varying rate of water
discharge from the auxiliary conduit.
10. A water balance control for a center pivot irrigation system,
according to claim 9, in which the main drive means includes a main
duty cycle timer for controlling the angular speed of the main
conduit assembly, in which the auxiliary speed control comprises an
auxiliary duty cycle timer, and in which the primary control means
connects the auxiliary duty cycle timer in series with the main
duty cycle timer.
11. A water balance control for a center pivot irrigation system,
according to claim 10, in which the setting of the auxiliary duty
cycle timer is determined in accordance with the relation
where
T = percent duty cycle
P.sub.H = maximum pressure head, all valve-controlled nozzles
closed
P.sub.L = minimum pressure head, all system nozzles open.
12. A water balance control for a center pivot irrigation system,
according to claim 10, in which the setting of the auxiliary duty
cycle timer is determined in accordance with the relation
where
T = percent duty cycle
P.sub.h = maximum pressure head, all valve-controlled nozzles
closed
P.sub.l = minimum pressure head, all system nozzles open.
13. A water balance control for a center pivot irrigation system,
according to claim 4, in which the sensing means comprises a cam
shaft, a mechanical linkage interconnecting the main conduit
assembly and the auxiliary conduit assembly with the cam shaft to
rotate the cam shaft in accordance with movements of the auxiliary
conduit assembly relative to the outer end of the main conduit
assembly, and a direction sensing cam member frictionally coupled
to the cam shaft for movement between two limit positions
indicative of movement of the auxiliary conduit assembly in
swing-in and swing-out directions, respectively, and in which the
secondary control means comprises a selector device actuated by the
direction sensing cam member.
14. A water balance control for a center pivot irrigation system,
according to claim 13, in which each primary control circuit
comprises a cam-operated control device actuated by an individual
cam on the cam shaft.
15. A method of water balance control for a center pivot irrigation
system of the kind including an elongated main conduit assembly
having an inner end pivotally connected to a water source at a
central pivot point and having a plurality of discharge nozzles at
spaced intervals along its length, main drive means for moving the
main conduit assembly around the pivot point to irrigate a primary
field area of circular configuration, an elongated auxiliary
conduit assembly having an inner end connected to and movable with
the outer end of the main conduit assembly and having a series of
discharge nozzles at spaced intervals along its length, and
auxiliary drive means for moving the auxiliary conduit assembly
over a range between a fully contracted position and a fully
extended position, relative to the main conduit assembly, to
irrigate at least one secondary field area beyond the periphery of
the primary field area, water balance control method comprising the
steps of:
sensing angular movements of the auxiliary conduit assembly, within
its range, relative to the outer end of the main conduit
assembly,
and regulating the rate of water discharge from the auxiliary
conduit nozzles in accordance with the position and direction of
movement of the auxiliary conduit assembly within its range by
actuating the individual discharge nozzles of the auxiliary conduit
assembly between closed and maximum open conditions in accordance
with two predetermined programs, one for swing-out motion and one
for swing-in motion of the auxiliary conduit assembly.
16. A method of water balance control for a center pivot irrigation
system, according to claim 15, including the additional step of
regulating the angular speed of the main conduit assembly whenever
the system pressure varies significantly as a result of a varying
rate of water discharge from the auxiliary conduit.
17. A method of water balance control for a center pivot irrigation
system, according to claim 16, in which the angular speed of the
main conduit is reduced, whenever a given number of discharge
nozzles of the auxiliary conduit assembly are open, approximately
in accordance with the relation
where
T = percent duty cycle for reduced angular speed
P.sub.L = minimum pressure head, all system nozzles open
P.sub.H = maximum pressure head, all valve-controlled nozzles
closed.
18. A method of water balance control for a center pivot irrigation
system, according to claim 15, including the additional step of
reversing the programs for swing-in and swing-out motion for a
reversal of direction of angular movement of the main conduit
assembly.
Description
BACKGROUND OF THE INVENTION
Center pivot irrigation systems, of which Zybach U.S. Pat. No.
2,941,727 is a relatively early example, are widely used for
irrigation of large agricultural areas. The lengths of commercial
systems of this kind range from about 200 feet to over 1800 feet.
In any such system, because the central portion of the radially
extending main conduit moves much more slowly than the outer
portion, it is necessary and customary to provide for a
substantially larger discharge of water at the outer end of the
system than at the inner end. Typically, this control is exercised
by a gradation of the orifice sizes for the sprinklers or discharge
nozzles, using small discharge orifices at the inner portion of the
system and substantially larger orifices at the outer end. Another
water balance technique that has been applied to basic center pivot
irrigation systems entails programmed time control for discharge
nozzles of uniform size; a water balance control of this particular
kind is disclosed in Chapman U.S. Pat. No. 3,901,422.
The conventional center pivot irrigation system covers a circular
area; in a rectangular field, the corners are not irrigated. For a
number of years, it has been customary to irrigate a part of the
corner areas by means of a large high volume long distance
discharge nozzle called an end gun. The end gun is maintained
inoperative as the system sweeps past those parts of the field
where the arc described by the outer end of the pivoting main
conduit approaches relatively close to the edges of the field. The
end gun is operated for limited arcuate segments of movement of the
system that are aligned with the corners. The end gun is usually
turned on and off by a relatively simple circular cam mounted at
the central pivot, with adjustable cam members to determine the
arcuate limitations for the system at which the end gun is
actuated.
More recently, center pivot irrigation systems have been provided
with an auxiliary conduit that is pivotally mounted to the outer
end of the main conduit. The auxiliary conduit, sometimes called a
boom, is held at an angle of close to 90.degree. to the main
conduit and is maintained essentially inactive during those
intervals in which the outer end of the main conduit is moving
closely adjacent the edge of the area to be irrigated. In
irrigating the corners of a rectangular field, or in irrigating
other areas, in which a part of the area is located beyond the arc
described by the end of the main conduit, the auxiliary conduit is
pivoted outwardly to an angle of greater than 90.degree. and water
is discharged through the auxiliary conduit to irrigate an
additional area beyond the boundary of the area that would normally
be covered by the system. An early example of this more recent type
of center pivot irrigation system is described in Seckler et al.
U.S. Pat. No. 3,802,627. Controls for directing the movements of
the auxiliary conduit or boom are described in Kircher et al. U.S.
Pat. No. 3,797,517 and in Daugherty et al U.S. Pat. No. 3,902,668.
The Daugherty et al patent is particularly advantageous, as regards
a steering system for the auxiliary conduit boom, because it allows
for ready and effective avoidance of obstructions and for the
irrigation of peripheral areas of widely varying configuration.
The addition of a pivotal auxiliary conduit at the outer end of a
conventional center pivot irrigation system, however, introduces
substantial problems with respect to maintenance of water balance
in the areas irrigated both by the main conduit and the auxiliary
conduit. In particular, the area covered by the auxiliary conduit
as it swings outwardly from a first angular alignment to a second
angular alignment relative to the end of the boom is substantially
different from the area that must be irrigated by the same
auxiliary conduit as it swings inwardly through the same angular
distance. Furthermore, the differences between the two areas vary
in dependence upon the direction in which the main conduit rotates,
as compared with the direction in which the auxiliary conduit
extends from the main conduit. Finally, with an auxiliary conduit
of any substantial length, an increased discharge from the
auxiliary conduit produces a reduced discharge from the main
conduit as the result of the pressure/discharge characteristics of
the pumps ordinarily used to supply water to systems of this
general kind, necessitating a system speed adjustment to maintain
adequate water balance in the area covered by the main conduit.
SUMMARY OF THE INVENTION
It is a principal object of the invention, therefore, to provide a
new and improved water balance control for a center pivot
irrigation system of the kind equipped with a pivotally movable
auxiliary conduit extension employed to irrigate areas beyond the
periphery of the main conduit of the system.
Another object of the invention is to provide a new and improved
water balance control for an auxiliary conduit extension on a
center pivot irrigation system, which control effectively
compensates for the differences in the areas covered by the
auxiliary conduit in swing-out and swing-in movements relative to
the outer end of the main conduit.
Another object of the invention is to provide a water balance
control for an auxiliary conduit extension pivotally connected to
the outer end of a center pivot irrigation system that can be
quickly and easily changed to correct for changes in the direction
of rotational movement of the main conduit of the system, without
requiring re-programming of the control.
An additional object of the invention is to provide a new and
improved water balance control for a center pivot irrigation system
of the kind including a rotatable main conduit with an auxiliary
conduit pivotally connected to its outer end that effectively
compensates for losses in pressure head in the main conduit
occasioned by the discharge of water from the auxiliary
conduit.
A specific object of the invention is to provide a new and improved
water balance control for a pivotal auxiliary conduit extension on
a center pivot irrigation system that is simple and inexpensive in
construction, reliable in operation, and directly adaptable to a
wide variety of systems of varying overall length.
Accordingly, the invention relates to a water balance control for a
center pivot irrigation system of the kind including an elongated
main conduit assembly having an inner end pivotally connected to a
water source at a central pivot point and having a plurality of
discharge nozzles at spaced intervals along its length, main drive
means for moving the main conduit assembly around the pivot point
to irrigate a primary field area of circular configuration, an
elongated auxiliary conduit assembly having an inner end connected
to and movable with the outer end of the main conduit assembly and
having a series of discharge nozzles at spaced intervals along its
length, and auxiliary drive means for moving the auxiliary conduit
assembly over a range between a fully retracted position and a
fully extended position, relative to the main conduit assembly, to
irrigate at least one secondary field area beyond the periphery of
the primary field area. The water balance control comprises sensing
means for sensing movement of the auxiliary conduit assembly,
within its range, relative to the outer end of the main conduit
assembly, and primary control means, actuated by the sensing means,
for regulating the rate of water discharge from the auxiliary
conduit nozzles in accordance with the position and direction of
movement of the auxiliary conduit assembly within its range.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective elevation view of a center pivot irrigation
system of the kind in which the water balance control of the
present invention may be incorporated;
FIG. 2 is a schematic plan view of the center pivot irrigation
system of FIG. 1 as employed in irrigating a field of a given
configuration;
FIG. 3 is a schematic plan view of the center pivot irrigation
system of FIG. 1 as applied to the irrigation of an unobstructed
rectangular corner of a field;
FIG. 4 is a schematic plan view similar to FIG. 3 showing the
system irrigating a field corner which includes an obstruction of
substantial size;
FIG. 5 is a detail plan view of the auxiliary conduit assembly of
the irrigation system of FIGS. 1-4, including a schematic
illustration of a part of the water balance control of the present
invention.
FIG. 6 is a partial schematic plan view illustrating the preferred
pattern covered by the end guns of the corner pivot irrigation
system of FIGS. 1-5;
FIG. 7 is a simplified block diagram of a water balance control
constructed in accordance with one embodiment of the present
invention;
FIG. 8 is a schematic illustration of one form of apparatus that
may be utilized to implement the water balance control in FIG.
7;
FIG. 9 is a detail elevation view illustrating the principal
components of the electrical controls shown in FIG. 8; and
FIG. 10 is a simplified sectional view taken approximately along
line 10-10 in FIG. 9.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
FIG. 1 illustrates a center pivot irrigation system 10 constituting
one example of the kind of system in which the water balance
control of the present invention may be employed. System 10
includes an elongated main water conduit assembly 20 comprising a
main conduit 29 having an inner end pivotally connected to a
central water supply point 12 that is connected to a water source
11. Conduit 29 is supported by a plurality of self-propelled
support towers 21, each including a pair of wheels 22 driven by a
motor 23 mounted on the support tower framework 24. The motors 23,
in the illustrated system, are preferably electric motors, but
water-drive motors, other hydraulic motors, or pneumatic motors
could be employed. Trusses 25 aid in support of the main water
conduit 29.
The main water conduit 29 of assembly 20 comprises a plurality of
segments 29A, 29B, 29C, etc. extending out to the end segment 29J
(see FIG. 2). These segments extend from the central pivot point 12
to support towers 21A, 21B, 21C, etc. up to the end support tower
21J of assembly 20. The essentially rigid conduit segments are each
flexibly connected to the adjacent conduit segments at the support
towers. Each of the conduit segments 29A-29J has a plurality of
water discharge nozzles 28 at spaced intervals along its
length.
An elongated auxiliary conduit assembly 30 is pivotally connected
to the outer end of the main water conduit assembly 20, at tower
21J, by a joint 40. Assembly 30, sometimes referred to herein as a
boom, includes an auxiliary water conduit 32 connected with the
main water conduit 29 of assembly 20 by a connecting conduit 39.
One self-propelled steerable support tower 31 is shown, for boom
30; additional support towers can be used, depending on the length
of the boom. For an auxiliary conduit 32 of relatively short
length, the entire boom 30 may be of cantilever construction,
supported from the end tower 21J of the main conduit assembly
20.
A single or dual end gun is preferably mounted at the outer end of
the auxiliary water conduit 32. A dual end gun arrangement,
comprising an outer limited-angle end gun 33 and an adjacent
full-circle end gun 34, is illustrated. The auxiliary conduit 32
has a series of water discharge nozzles 35 at spaced intervals
along its length. End guns 33 and 34 provide for irrigation beyond
the outermost end of boom 30.
As shown in FIG. 2, the main water conduit assembly 20 irrigates a
circular area in a field 14 bounded by the line 50, supplying water
thereto through the discharge nozzles 28 (FIG. 1). The boom support
tower 31 can be controlled by an antenna 41 and suitable steering
controls (not shown) so that its wheels 37 follow a guidance wire
13 buried in the periphery of field 14; wire 13 is connected to a
signal source 15. Thus, the outer end of conduit 32 follows a path
as defined by line 51. By controlling the end guns 33 and 34, an
additional area can be covered as shown by line 52. The total area
effectively irrigated by system 10 is shown by the area within line
52. This irrigated area is modified to avoid obstructions 53 and
extends well into the corners 54, 55, 56 and 57 of field 14.
Movement of the main conduit assembly 20 is accomplished by main
drive means comprising the motors 23 on towers 21, and appropriate
motor controls, which may be generally conventional in construction
and operation. The wheels 37 of the boom support tower 31 may be
provided with individual drive motors 36 essentially similar to the
propulsion motors 23 used for the main conduit towers 21. Constant
speed motors are preferred.
When the auxiliary water conduit assembly 30 is in its fully closed
or tuck position, as when system 10 traverses area 58, the motors
on end support tower 21J may be driven continuously or in
accordance with a fixed duty cycle. When a certain amount of
deflection is sensed by a suitable sensor (not shown) at the joint
above the adjacent inner support tower 21I, the motor of tower 21I
is driven for a limited period to straighten out the joint. This
method of control continues through adjacent segments of the main
conduit assembly 20. Each inwardly displaced support tower is
driven less as central point 12 is approached; the innermost
support tower 21A is driven least. Strain sensors at the joints in
the main conduit 29 can be used instead of deflection sensors, if
desired.
The auxiliary drive means for boom 30, comprising motors 36, wheels
37, and suitable motor controls (not shown), may be activated or
stopped according to a signal from a strain sensor (not shown) at
the joint 40. When the main conduit assembly 20 has moved forward
and created a strain at joint 40, support tower 31 is signalled to
drive forward until the stress is alleviated. The sensor may also
afford a complete shut off of all towers, as a safety precaution,
for a given excess stress condition at joint 40.
Alternatively, the motors 36 for boom support tower 31 can be
driven continuously, or in accordance with a fixed duty cycle, and
the strain signal at joint 40 may be utilized to drive support
tower 21J. That is, either of the towers 21J and 31 can be employed
as a master tower, with the other towers following accordingly.
FIGS. 3 and 4 are detailed schematics showing the positions of the
main conduit assembly 20 and the auxiliary conduit assembly 30 at
various points during traversal of a normal square corner (FIG. 3)
and an obstructed corner (FIG. 4). Each figure shows the outer
circumference 50 of the travel of the main conduit assembly 20. The
path 51 followed by the outer end of the boom 30 is also shown; the
maximum coverage of irrigation is illustrated in each figure by
line 52. The outer limit of the field in each figure is shown by
line 70. Boom 30 describes an angle B.sub.min of approximately
90.degree. with respect to the main conduit assembly 20 at the
maximum closed or tuck positions, 20A, 30A. The maximum angle
B.sub.max is preferably about 160.degree.. In the areas 71, the
auxiliary conduit assembly 30 is not swung out as rapidly as
possible; this is done to assure adequate water distribution
uniformity. The smoother the curves formed by path 51, the less the
stress on joint 40.
In a preferred mode of operation, end support tower 21J is the
master drive unit for the system 10. Tower 21J is driven in
accordance with a fixed duty cycle dependent upon the water
requirements of the field (this may be a continuous duty cycle,
when boom 30 is not swung out) and is driven in accordance with a
reduced duty cycle while boom 30 is extended. This allows a reduced
rate of travel for tower 21J when aligned with the corner of a
field, or in another area where boom 30 is extended, while still
permitting use of an inexpensive constant-speed motor for the
tower. Conversely, as noted above, the boom tower 31 may be used as
the master drive unit instead of tower 21J.
The center pivot irrigation system 10, as thus far described,
corresponds basically to the system set forth in Seckler et al.
U.S. Pat. No. 3,802,627, modified to include the buried wire
steering system for the auxiliary conduit assembly 30 that is
disclosed in Daugherty et al. U.S. Pat. No. 3,902,668. The water
balance control of the present invention, as described in detail
hereinafter, may also be utilized in conjunction with a center
pivot system employing a boom guidance apparatus of the kind
disclosed in the aforementioned Seckler et al. U.S. Pat. No.
3,802,627 or the control described in Kircher et al. U.S. Pat. No.
3,797,517, or virtually any other guidance apparatus for the
auxiliary conduit assembly 30, regardless of whether the auxiliary
conduit is of cantilever construction or employs a separate support
tower as illustrated in FIGS. 1 and 2.
In irrigating the corner of a rectangular field, if it is assumed
that the auxiliary conduit assembly 30 extends counterclockwise
from the main conduit assembly 20 and that the main conduit
assembly is rotating in a clockwise or "forward" direction (FIG.
3), system 10 approaches the corner with the two conduit assemblies
aligned as indicated by elements 20A and 30A in FIG. 3. This is the
tuck position for the auxiliary conduit assembly, with that
assembly at a minimum angle B with respect to the main conduit
assembly. This angle, designated B.sub.min in FIG. 3, is usually
approximately 90.degree.. .
As the main conduit assembly 20 continues its movement toward the
corner of the field, boom 30 begins to swing outwardly from the end
of the main conduit assembly 20, enlarging angle B. The maximum
B.sub.max for the angle B is attained at or slightly beyond an
orientation of 45.degree. for the main conduit assembly; see FIG.
3, orientation 20X. This is the fully extended position for boom
30; the angle B.sub.max is preferably somewhat less than
180.degree., usually about 160.degree..
As the main conduit assembly 20 moves from the position 20B to the
position 20C (FIG. 3), the angle at joint 40 changes from B1 to B2
as the auxiliary conduit assembly 30 traverses the cross-hatched
sector 81 between its positions 30B and 30C. As system 10 leaves
the corner area, it passes through the alignments 20D,30D and
20E,30E. For the alignment 20D,30D, the angle at joint 40 is again
equal to the angle B2. When the orientation 20E,30E, is reached,
the angle is again equal to the angle B1. During this movement, the
sector 82 is irrigated by water from the auxiliary conduit assembly
30.
As is clearly apparent in FIG. 3, the two sectors 81 and 82
irrigated by the auxiliary conduit assembly 30 during transition
between the two angles B1 and B2 are substantially different; the
area of sector 81 is much larger than for sector 82. This
illustrates the substantial difference between the water volume
requirements for swing-out movements and swing-in movements of boom
30. Unless provisions are made for effective regulation of the
water output of the auxiliary conduit assembly 30, for these two
different conditions, sector 81 will receive substantially less
water per unit area than sector 82 and neither of the two sectors
is likely to be kept in balance with the irrigation effected by the
main conduit assembly 20 within line 50. That is, an effective
water balance for those portions of the field irrigated by boom 30
will not be maintained.
The water balance problem described above in connection with FIG. 3
also occurs in relation to movements of the auxiliary conduit
assembly 30, relative to the main conduit assembly 20, in avoiding
obstructions. As shown in FIG. 4, the angle B3 between the
auxiliary conduit assembly 30 and the main conduit assembly 20 may
be the same for the two positions 20F,30F, and 20I,30I, whereas the
angle B4 may be attained at the two system orientations 20G,30G,
and 20H,30H. However, the sector 83 irrigated by boom 30 in moving
between positions 30F and 30G is substantially larger than the area
84 irrigated by the boom as it moves between positions 30H and
30I.
To afford an effective water balance throughout the area covered by
boom 30, the present invention provides sensing means for sensing
movements of the boom, within the range defined by the minimum tuck
angle B.sub.min and the maximum extension angle B.sub.max. In
sensing this movement, the sensing means inherently affords a
measure of the variations in the radial distance R (FIGS. 3 and 4)
between the arc 50 described by the outer end of the main conduit
assembly and the path 51 followed by the outer end of the auxiliary
conduit assembly 30. In accordance with the invention, the sensing
means is employed to actuate a primary control that regulates the
rate of water discharge from the nozzles 33, 34 and 35 and of the
auxiliary conduit assembly 30 (FIG. 1), in accordance with the
position of the auxiliary conduit assembly 30 within this range
B.sub.min - B.sub.max (R.sub.min - R.sub.max).
In addition, to afford a more accurate water balance, provision is
made for actuation of a secondary control means, by the sensing
means, that regulates the rate of water discharge from the nozzles
33, 34 and 35 of the auxiliary conduit assembly 30 in accordance
with the direction of relative movement of boom 30 within its
operating range. That is, whenever the auxiliary conduit assembly
30 swings out, away from its minimum tuck position and toward its
maximum extended position, as in the movement from alignment
20B,30B to orientation 20C,30C (FIG. 3), the rate at which water
discharge is increased is programmed differently from the rate at
which water discharge is decreased when the boom moves from
orientation 20D,30D to position 20E,30E, even though the same
angular change (between angles B1 and B2) occurs. In this way, the
differential between the areas of sectors 81 and 82 is compensated
and an overall water balance is maintained.
The same technique is applied in the situation illustrated in FIG.
4 with the system moving through the positions 20F,30F through
20I,30I, to compensate for the changes in area covered by boom 30,
for a given change in the angle B, that occurs as the result of a
reversal in the direction of angular movement of the auxiliary
conduit assembly 30 within its overall range. That is, the water
balance compensation for sectors 83 and 84 is effected in the same
manner as in relation to the areas 81 and 82 of FIG. 3.
FIG. 5 illustrates an exemplary construction that may be employed
for the auxiliary water conduit 32. The illustrated construction
provides a total of 10 discharge nozzles 35, numbered 35-1 through
35-10, located at spaced intervals along conduit 32. Two of these
sprinklers, nozzles 35-6 and 35-10, are of standard construction
and remain open whenever the irrigation system 10 is in operation.
The remaining nozzles 35-1 through 35-5 and 35-7 through 35-9,
however, are each equipped with a control valve actuated by a valve
control unit 87. The two end guns 33 and 34 are positioned at the
outer end of the auxiliary conduit 32. The end guns themselves
remain open at all times. However, a valve 88 is interposed in the
connection between the end guns and the remainder of conduit 32.
Valve 88 is actuated by the valve control unit 87.
For forward movement of the auxiliary conduit assembly 30 (see
FIGS. 3 and 4), utilizing an auxiliary conduit 32 having an overall
length of about 255 feet, one practical and effective sequence for
operation of the nozzles and end guns of conduit 32, as illustrated
in FIG. 5 is:
TABLE I ______________________________________ FORWARD MODE
SEQUENCING ______________________________________ Boom 30 Swinging
Out Boom 30 Swinging In Nozzle Distance R Distance R Nozzle On*
(feet) Sequence (feet) Off* ______________________________________
35-3 35 First 235-Variable End Guns 35-5; 35-7 45 Second 230 35-1
35-9 75 Third 215 35-4; 35-8 35-2 90 Fourth 210 35-2 35-4; 35-8 110
Fifth 160 35-9 35-1 125 Sixth 135 35-5; 35-7 End Guns 130-Variable
Last 60 35-3 ______________________________________ *Nozzles 35-6
and 35-10 are on continuously.
This sequence is controlled by the valve control unit 87. The
reason a variable displacement is indicated for the end guns 33 and
34, in Table I, is that the opening of the valve 88 that controls
the two end guns must require adjustment to preclude discharging
water onto obstructions, such as the obstructions 53 in FIG. 2, or
onto any road or the like situated immediately adjacent the
periphery of the field being irrigated.
Referring again to FIGS. 3 and 4, it is seen that the water balance
differential, relative to swing-out or swing-in movement of the
auxiliary conduit assembly 30, is reversed if the direction of
rotation of the main conduit assembly 20 is in a "reverse"
direction, the counterclockwise direction in FIGS. 3 and 4. For
this reverse mode of operation, the sequencing for the nozzles 35
and the end guns 33 and 34 of the auxiliary conduit 32 illustrated
in FIG. 5 is:
TABLE II ______________________________________ REVERSE MODE
SEQUENCING ______________________________________ Boom 30 Swinging
Out Boom 30 Swinging In Nozzle Nozzle On* Distance R Sequence
Distance R Off* ______________________________________ 35-3 60
First 130-Variable End Guns 35-5; 35-7 135 Second 125 35-1 35-9 160
Third 110 35-4; 35-8 35-2 210 Fourth 90 35-2 35-4; 35-8 215 Fifth
75 35-9 35-1 230 Sixth 45 35-5; 35-7 End Guns 235-Variable Last 35
35-3 ______________________________________ *Nozzles 35-6 and 35-10
are on continuously.
The designation of forward and reverse directions, in the foregoing
description, is quite arbitrary, and is dependent upon whether the
boom 30 extends to the left of the main conduit assembly 20, as
shown in the drawings, or in the opposite direction to the right of
the main conduit assembly. If this relationship is reversed, the
designation of the forward and reverse directions must also be
reversed.
The irrigation pattern of the two end guns 33 and 34 is illustrated
schematically in FIG. 6. As shown therein, gun 33 covers a limited
arc D (approximately 90.degree.) with the major portion of the arc
oriented ahead of the outer end of auxiliary conduit assembly 30,
assuming that the system is moving in a forward direction. The
other gun 34 covers a complete circular sector 89. However, other
end gun arrangements can be utilized as desired, depending in part
upon the number and spacing of the discharge nozzles along the
remaining length of boom 30.
FIG. 7 affords a block diagram of a water balance control 90
constructed in accordance with one embodiment of the present
invention. The water balance control 90 comprises an auxiliary
conduit movement sensor 91 that is mechanically connected to the
main conduit 29 and to the auxiliary conduit 32. Sensor 91 has an
output connection to a plurality of primary control circuits 92
that are utilized to control operation of the discharge nozzles of
conduit 32 whenever the auxiliary conduit is pivoted outwardly of
the main conduit (arrow X). Sensor 91 also has an output connection
to another primary control circuit unit 93 that incorporates
control circuits for regulating the output of the boom nozzles
whenever the auxiliary conduit 32 swings inwardly toward the main
conduit 29 (arrow Y).
The swing-out control unit 92 may comprise as many individual
control circuits as there are discharge nozzles on the auxiliary
conduit 32 (see FIG. 5). For the present example, however, there
are a total of seven individual nozzle control circuits. These
include one control circuit for each of the nozzles 35-1, 35-2,
35-3, and 35-9, plus one for valve 88 controlling the end guns 33
and 34. Of the two remaining control circuits, one actuates the
nozzles 35-4 and 35-8, while the other controls the nozzles 35-5
and 35-7. Thus, the control circuits in unit 92 are correlated with
the control elements of the nozzle control valve unit 87.
The other primary control circuit unit, swing-in unit 93, includes
a plurality of individual control circuits, corresponding in number
to those in unit 92, all of which are connected to the nozzle valve
control unit 87.
The water balance control 90 of FIG. 7 further comprises a
secondary control circuit 94 linked to sensor 91. Device 94
determines the direction in which the auxiliary conduit 32 is
moving, or has last moved, with respect to the main conduit 29,
either a swing-out movement (arrow X) or a swing-in movement (arrow
Y). The secondary control circuit 94 is connected to each of the
two primary control circuit units 92 and 93. When the auxiliary
conduit 32 swings out, the direction selector control circuit 94
actuates the primary control circuits of unit 92 so that those
circuits in turn can actuate the nozzle control valve unit 87 to
regulate water discharge from auxiliary conduit 32. Conversely,
when the auxiliary conduit swings in toward the main conduit (arrow
X), the direction selector control 94 actuates the primary control
circuits 93 to maintain control of the nozzle control valves of
unit 87. In this manner, the secondary control circuit 94 is
employed to regulate the water discharge from the auxiliary conduit
nozzles in accordance with the direction of relative movement of
the auxiliary conduit assembly 30 within its range between the
angles B.sub.min - B.sub.max, corresponding to the radial distance
range R.sub.min - R.sub.max (FIG. 3).
The water balance control 90 of FIG. 7 also includes a speed
control unit 96 having two inputs, one input from each of the
primary control circuit units 92 and 93. Speed control 96 is in
turn connected to a main conduit drive control 97 that regulates
the speed of rotation of the main conduit assembly 20. Speed
control 96 may comprise a conventional adjustable duty cycle timer.
If the main conduit drive control 97 includes a duty cycle
(percent) timer, the two timers are connected in series. Speed
control 96 is utilized to reduce the speed of the main conduit
assembly 20 whenever the boom 30 has been extended outwardly to a
predetermined extent, as described more fully hereinafter.
FIG. 8 affords a simplified schematic diagram of one kind of
apparatus that may be utilized in implementation of the water
balance control 90 illustrated in FIG. 7. The water balance control
90A illustrated in FIG. 8 comprises an auxiliary conduit movement
sensor 91A including a rod 101 having one end 102 pivotally
connected to the auxiliary conduit 32 at joint 40. The other end
103 of rod 101 is pivotally connected to a drive sprocket 104. A
drive chain or gear belt 105 engages sprocket 104 and also engages
a driven sprocket 106 mounted upon a shaft 107. Thus, the angular
position of shaft 107, at any given time, is indicative of the
angular position of auxiliary conduit 32 relative to main conduit
29. Further, the direction in which shaft 107 rotates, at any given
time, is indicative of the direction of movement of the auxiliary
conduit with respect to the main conduit, either swinging in or
swinging out.
The secondary control circuit or direction selector 94A illustrated
in FIG. 8 comprises a single-pole double-throw sensor switch 111
that is mechanically connected to shaft 107. The preferred form of
mechanical connection is a friction clutch, such as described in
connection with FIG. 9. Switch 111 has a normally open terminal 112
and a normally closed terminal 113. The normally open terminal 112
is connected to the operating coil 114 of a relay comprising a
plurality of single-pole double-throw contacts; only two of the
relay contacts, 115-1 and 115-9, are illustrated.
The normally closed terminal of relay contact 115-1 is connected to
a cam actuated switch 92A-1 that constitutes one of the primary
control circuits for swing-out operation of the auxiliary conduit
32 (see FIG. 7). The normally open side of contact 115-1 is
connected to a similar cam actuated switch 93A-1. The two switches
92A-1 and 93A-1 are each connected to the solenoid 117-1 of a
solenoid-operated pilot valve 118-1. Solenoid 117-1 and valve 118-1
are both part of the nozzle control valve unit 87A for the water
balance control 90A.
The normally closed terminal of relay contact 115-9 is connected to
a cam actuated switch 92A-9 that is in turn connected to a solenoid
117-9 in unit 87A. Solenoid 117-9 is employed to actuate a pilot
valve 118-9. The normally open side of contact 115-9 is connected
to a cam actuated switch 93A-9 that is also connected to solenoid
117-9. The common terminals of relay contacts 115-1 through 115-9
are connected to a suitable power supply.
Each of the two pilot valves 118-1 and 118-9 has an inlet port
connected to auxiliary conduit 32. The outlet port of valve 118-1
is connected by a tube 119-1 to a hydraulically actuated valve
121-1 that is interposed in the connection between nozzle 35-1 and
auxiliary conduit 32. Similarly, the outlet port of valve 118-9 is
connected by a tube 119-9 to a hydraulic pilot actuated valve 121-9
interposed between conduit 32 and nozzle 35-9. By comparing FIGS. 5
and 8, the pattern of control connections for all of the nozzles on
auxiliary conduit 32 can be ascertained.
All of the cam actuated primary control switches 92A-1 through
92A-9 and 93A-1 through 93A-9 (FIG. 8) are mechanically connected
to shaft 107 of the auxiliary conduit movement sensor 91A. In the
preferred construction illustrated in FIGS. 9 and 10, the cams for
actuating the switches are mounted directly upon shaft 107. Thus,
by adjusting the cams, these control switches can be made to open
and close in direct relationship to desired angular orientations of
shaft 107, which are representative of the angular orientation of
auxiliary conduit 32 relative to main conduit 29.
In considering the operation of water balance control 90A (FIG. 8),
it may first be assumed that the auxiliary conduit 32 is moving
outwardly of the main conduit 29 (arrow X). Under these conditions,
switch 111 remains in the illustrated position and the relay
operating coil 114 remains unenergized so that relay contacts 115-1
and 115-9 are in the positions shown. As the auxiliary conduit
continues its swing-out movement, shaft 107 rotates to reflect that
movement. Switch 111 does not change, but remains in the position
shown.
Assuming that the water balance control 90A has been adjusted to
operate in accordance with the sequence set forth in Table I, and
that the system is operating in the forward mode, switch 92A-9 is
opened by its associated cam when the auxiliary conduit has moved
far enough outwardly so that the distance R (see FIG. 3) is 75
feet. This de-energizes solenoid 117-9, closing valve 118-9 and
interrupting the supply of water under pressure through tube 119-9.
This opens valve 121-9 and turns on discharge nozzle 35-9. Later,
as the auxiliary conduit continues its outward swinging movement,
switch 92A-1 is opened when the distance R is approximately one
hundred twenty-five feet (see Table I). As a consequence, solenoid
117-1 is de-energized, closing valve 118-1 and interrupting the
supply of water through tube 119-1 to valve 121-1. This opens valve
121-1 and initiates a discharge from nozzle 35-1. Similar circuits,
which have not been illustrated in FIG. 8, actuate the other
nozzles of the boom 30 in accordance with a complete swing-out
sequence set forth in Table I.
During a normal swing-out movement of auxiliary conduit 30 to its
full extended position, the swing-in control switches 93A-1 through
93A-9 all open. The angular orientations at which they open are not
critical for swing-out movement, however, since these switches are
all effectively disconnected at the relay contacts 115-1 through
115-9 during the swing-out operation.
When boom 30 starts to swing back in (arrow Y), the friction clutch
connection from shaft 107 to switch 111 actuates the switch and
completes an energizing circuit for relay coil 114. As a
consequence, each of the relay contacts 115-1 through 115-9 is
actuated from its normally closed position to its normally open
position, so that power supply connections to solenoids 117-1
through 117-9 must now be made through control switches 93A-1
through 93A-9 instead of switches 92A-1 through 92A-9.
With the auxiliary conduit swinging in, it is necessary to reduce
the rate of water discharge more rapidly than that discharge rate
was increased during swing-out operation, for the reasons discussed
above in connection with FIGS. 3 and 4. Consequently, and in
accordance with the sequence of Table I, when the inward swinging
movement of auxiliary conduit 32 reaches a point at which the
radial distance R is 230 feet, switch 93A-1, which has previously
been open, closes. This restores the energizing circuit for
solenoid 117-1 and opens valve 118-1 so that its output to valve
121-1 is restored. As a consequence, valve 121-1 closes and nozzle
35-1 is shut off. Similarly, when the boom has swung inwardly to a
point at which the distance R is approximately 160 feet, switch
93A-9 closes to energize solenoid 117-9. This opens pilot valve
118-9, restoring the hydraulic circuit to valve 121-9 and closing
that valve to shut off nozzle 35-9. In this manner, the complete
sequence of Table I can be carried out.
The foregoing description of operation of water balance control
90A, FIG. 8, has been based upon the assumption that the main
conduit assembly 20 has been rotated in the forward direction
(FIGS. 3 and 4) with the auxiliary conduit assembly 30 trailing
behind the main conduit assembly 20. For operation with the main
conduit assembly rotating in the reverse direction, pushing the
boom ahead of it, it is necessary to utilize the reverse mode
sequence of Table II. This is accomplished, without changing any of
the cams for the control switches 92A-1 through 92A-9 or 93A-1
through 93A-9, with a simple electrical change in the secondary
control, the direction selector 94A. Thus, to change from the
forward sequence of Table I to the reverse sequence of Table II in
accordance with a change in the direction of rotation of the main
conduit assembly, the connection of the relay coil 114 is changed
from contact 112 to contact 113 of switch 111, as by means of a
reversing switch 125. This single simple change, without more,
prepares the system for operation in the reverse mode.
The control circuits for speed control 96 (FIG. 7) can be
duplicates of the circuits described for the auxiliary conduit
nozzles, and hence have not been illustrated in FIG. 7. In one
commercial embodiment of the water balance control of the
invention, the sequence control for speed unit 96 is actuated by
the same circuits that control nozzle 35-9.
FIGS. 9 and 10 illustrate one physical construction that can be
utilized for the movement sensor 91A, for the direction sensing
switch 111 of the secondary control circuit 94A, and for the
primary control switches 92A-1 through 92A-9 and 93A-1 through
93A-9 in the water balance control 90A of FIG. 8. FIG. 9 shows the
drive sprocket 104 that is connected to the rod 101, in its
relation to the driven sprocket 106 affixed to shaft 107. As noted
above, the arrangement is such that the direction of angular
movement of shaft 107 reflects the direction of angular movement of
the auxiliary conduit relative to the main conduit and the angular
displacement of shaft 107 corresponds to the angular displacement
of the two conduits relative to each other. The mechanical
advantage afforded by the large sprocket 104 driving the small
sprocket 106 is employed merely to increase the overall angular
movement of the shaft 107 for the total range B.sub.min
-B.sub.max.
The primary control switches for swing-out movement of the
auxiliary conduit, switches 92A-1 through 92A-9, are mounted in a
vertical stack at one side of shaft 107. The primary control
switches 93A-1 through 93A-9 for swing-in movement of the auxiliary
conduit are mounted in another vertical stack adjacent shaft 107.
The angular orientation of the two stacks of switches is shown in
FIG. 10. The two stacks of switches are vertically staggered by a
small distance, as illustrated in FIG. 9.
For switch 92A-1, an adjustable cam 131 is mounted upon shaft 107.
A similar cam 141 on shaft 107 actuates switch 93A-1. Similarly, an
adjustable cam 139 on shaft 107 is employed to actuate switch 92A-9
and another adjustable cam 149 on that shaft actuates switch
93A-9.
As shown in FIG. 10, a typical cam 139 comprises a core element 151
affixed to shaft 107 for rotation therewith. Core 151 includes an
arm 152 on which a small worm member 153 is mounted. The worm 153
engages a series of gear slots 154 formed in the face of the cam
body 155. The adjustable cam 149 is of similar construction. It is
thus seen that the two cams can be adjusted relative to each other
so that the transition point 157 on cam 139 that actuates switch
92A-9 can be adjusted independently of the location of the
transition point 158 on cam 149 that actuates switch 93A-9.
At the upper end of shaft 107, FIG. 9, two bushings 161 and 162 are
mounted on shaft 107, the mounting arrangement employed being one
which permits axial movement of the bushings but compels the
bushings to rotate with rotation of shaft 107. A cam member 163 is
mounted on shaft 107 intermediate the bushings 161 and 162 and two
friction members 164 and 165, which may be fiber washers, are
interposed between cam 163 and bushings 161 and 162, respectively.
A spring 166 on shaft 107, extending axially between bushing 161
and a washer 167, biases bushing 161 downwardly, affording a
frictional coupling between shaft 107 and cam 163 through the two
bushings 161 and 162 and the friction members 164 and 165.
Cam 163 has an arm 168 which projects outwardly between two posts
171, and 172, limiting the rotational movement of cam 163. For this
construction, the sensing switch 111 comprises another small switch
that is positioned adjacent cam 163 to be actuated by that cam; the
switch has been omitted in FIG. 9 for clarity of illustration.
The operation of the primary control switches 92A-1 through 92A-9
and 93A-1 through 93A-9 will be evident from FIGS. 9 and 10 and
requires no explanation. With respect to the selector switch
actuated by cam 163, it can be seen that when the shaft 107 rotates
in a clockwise direction (arrow X' in FIG. 10), arm 168 engages
post 161. With the cam in that position, effected in response to
swing-out movement of auxiliary conduit 32, the switch 111 actuated
by cam 163 is held open, as shown in FIG. 8. Conversely, when shaft
107 rotates in a counterclockwise direction (arrow Y') arm 168
comes to rest against post 172. For this position of arm 168, and
cam 163, switch 111 is closed upon its contact 112 (FIG. 8) to
indicate that the auxiliary conduit is moving in a swing-in
direction. The transition point on cam 163, for opening and closing
its associates switch, is preferably adjusted to engage the switch
cam follower when the arm 168 is mid-way between posts 171 and
172.
The primary control circuits for the speed control device 96 (FIG.
7) may be of the same construction as for the discharge nozzles.
Thus, in a circuit like that of FIGS. 8-10, an additional pair of
cam switches associated with shaft 107 may be employed to actuate
the speed control, slowing down the rotational movement of the main
conduit assembly 20 when boom 30 is extended and a substantial
number of the extension discharge nozzles are operational.
Actuation is usually correlated with positioning of the auxiliary
conduit assembly beyond the mid-point of its range B.sub.min
-B.sub.max. In one commercial arrangement, using the nozzle
sequences of Tables I and II, the speed control device 96 is
actuated on and off in coincidence with actuation of nozzle 35-9,
utilizing the primary control switches 92A-9 and 93A-9.
Speed control 96 would be unnecessary if irrigation system were
connected to a water source 11 affording a constant head at any and
all system discharge rates. Ordinarily, however, such a
constant-head water supply is unavailable. For most water pumps,
the effective head decreases as a function of increased system
discharge rate; accordingly, when the nozzles of the auxiliary
extension assembly are open, the discharge rate from the main
conduit assembly is reduced, necessitating a slowdown of the main
conduit assembly if a reasonable water balance is to be maintained
in the central area 50 (FIGS. 2-4).
The main conduit drive control 97 (FIG. 7) ordinarily includes a
primary duty cycle (percent) timer than controls the rotational
speed of the main conduit assembly 20 by varying the duty cycle for
the end tower motor 23J; the period of revolution for the main
conduit assembly may vary from as low as ten hours to as much as
one week. In a system of this kind, the speed control 96 may
comprise a secondary duty cycle timer connected in series with the
primary timer. To determine the setting of the secondary duty cycle
timer, the highest pressure head P.sub.H at joint 40 is measured
with all valve-controlled auxiliary conduit discharge nozzles shut
off, and the lowest pressure head P.sub.L at joint 40 is measured
with all nozzles open. The percent duty cycle T is then determined
in accordance with the relation
1. T = .sqroot. P.sub.L /P.sub.H
or the closely equivalent relation
2. T = 1 - P.sub.H - P.sub.L /2 P.sub.H
Thus, for example, if P.sub.H = 75 psi and P.sub.L = 60 psi, the
duty cycle setting for speed control 96 is 89.5% by relation (1) or
90% by relation (2). Once this setting has been established, it may
remain unchanged. Adjustments for depth of coverage made at the
main duty cycle timer in drive control 97 are effectively applied
to the entire area covered by system 10.
For effective use of a particular sequencing program (e.g., the
program of Tables I and II), it is necessary to calibrate the
primary control circuits 92A and 93A (FIG. 8) in accordance with
the length of the main conduit assembly 20, since the radial
distance R varies, relative to the measured angle B1 when the main
conduit length is changed. This can be readily accomplished for all
standard lengths of the main conduit assembly, the calibration
being effected by adjustment of the cams that actuates the primary
control switches. An effective sequencing program for any given
construction for boom 30 (length of auxiliary conduit 32, number
and spacing of nozzles 35 and end guns, angular range B.sub.min
-B.sub.max, etc.) is best determined on an empirical basis,
although mathematical formulations can be employed in evaluating
the many variables involved. The program of Tables I and II applies
to an auxiliary conduit having a total length of about 255 feet
with a spacing of about 25 feet between nozzles 35 (see FIG.
5).
In the specific embodiment of FIGS. 8-10, a particular combination
of mechanical, electrical and hydraulic control elements is
employed. It will be recognized that other combinations may be
substituted; for example, the solenoids 117-1 through 117-9 could
actuate the valves 121-1 through 121-9 directly, without using the
intervening hydraulic pilot valves 118-1 through 118-9. The
specific controls described operate to actuate the auxiliary
conduit discharge nozzles on or off, with no intervening settings.
This mode of control is preferred. However, throttling controls
employing variable-orifice discharge nozzles may be utilized if
desired, and a similar continuous speed control can also be
employed instead of the described step speed control.
* * * * *